Trim Black Frames from a Video

About this tool

Videos often carry fully-black frames at the very start or end — a black leader before a recording begins, a fade-to-black outro, or dead frames left by a screen recorder or camera. They pad the runtime, throw off thumbnails and auto-play previews, and look sloppy on a re-upload. This tool finds those black edges automatically and trims the clip down to the real picture — in two passes, the same way video engineers do it by hand with ffmpeg:

1. Detect — ffmpeg's blackdetect filter scans every frame and logs each run of black it finds (black_start → black_end). We read that log to locate the leading black run (one that begins at the very start) and the trailing black run (one that ends at the very end).
2. Trim — the clip is cut to the non-black span and re-encoded with H.264 at CRF 18 (visually lossless tier); audio is re-encoded to AAC so it stays in sync at the exact cut points.

Everything runs in your browser via WebAssembly ffmpeg — the file is never uploaded. If there is no black at the ends you asked for, the tool tells you instead of re-encoding the clip unchanged.

Worked example

A 10-second screen recording that opens with 1.5 s of black (leader) and ends with a 1.8 s fade to black:

• the detect pass logs black_start:0 black_end:1.5 and black_start:8.2 black_end:10;
• the leading run starts at 0, so the new start is 1.5 s; the trailing run ends at 10, so the new end is 8.2 s;
• the trim pass keeps 1.5 s – 8.2 s, producing a 6.7-second clip with the black intro and outro gone.

Leave the defaults (pixel threshold 0.10, black-pixel ratio 0.98, min duration 0.10 s) for normal black edges. Set Trim which ends to Start only or End only to keep one side untouched. If your black is really dark grey (a heavily compressed fade), raise the pixel threshold toward 0.15; if a logo or timestamp sits over the black and keeps it from being detected, lower the black-pixel ratio toward 0.90.

Limits and edge cases

• Input is capped at 25 MB in chat/CLI; in the browser the practical limit is your device's memory.
• Only the two edges are trimmed. Black frames in the middle of the clip are kept — this tool never cuts the interior. (To remove every black segment, that's a different job.)
• A black run only counts as an edge when it starts within 0.25 s of the beginning or ends within 0.25 s of the end; a black run just inside the clip is treated as content.
• min duration is the shortest black run the detector reports. At the default 0.10 s a single black frame in a 24–30 fps clip may be too brief to catch — lower it (e.g. 0.04) to trim a one-frame flash.
• If the entire clip reads as black at your settings, the tool refuses to trim (nothing would remain) and suggests lowering the thresholds or raising the minimum duration.
• Trimming requires re-encoding (a stream copy can only cut on a keyframe), so the video track is always re-encoded; CRF 18 keeps that visually transparent. Output keeps the input container for MP4/MOV/M4V/MKV, otherwise it becomes MP4.

FAQ